The cache memory system 1 comprises: a virtual index obtaining unit 13 operable to obtain, based on a virtual address, virtual indexes of an access-target cache line and a cache line potentially having a cache-aliasing relationship with the access-target cache line; a physical tag obtaining unit 15 operable to obtain a physical tag of a physical page by performing address translation on the virtual address; and a comparing unit 16 operable to compare a physical tag TAG obtained by the physical tag obtaining unit 15 with each tag information piece TAG(i) belonging to cache lines corresponding to the virtual indexes and output from the tag array 11a based on the virtual indexes obtained by the virtual index obtaining unit 13, and determines a cache hit/miss.